Dehydrogenation of tetrahydrofuran and alkylsubstituted tetrahydrofurans

ABSTRACT

A dehydrogenation process for preparing furan and alkyl furans comprising subjecting the corresponding tetrahydrofuran to a temperature in the range of 200 to 450*C in contact with a catalyst of palladium on carbon.

United States Patent 91 Tumolo Dec. 31, 1974 Company, P.O. Box 426, Marcus Hook, Pa. 19061 [22] Filed: Sept. 26, 1972 [21] Appl. No.: 292,383

' 521 US. ci.....- 260/346.1 R [51] Int. Cl C07d 5/14 [58] Field of Search 260/3461 R [56] References Cited OTHER PUBLICATIONS Belskii et al., Doklady Akademii Nauk SSSR, Khimii,

Vol. 138, N0. 4, 1961, pp. 829-830.

Primary ExaminerHenry R. Jiles Assistant Examiner-Bernard I. Dentz Attorney, Agent, or Firm-George L. Church; Donald R. Johnson; Stanford M.Back

[ 5 7] ABSTRACT A dehydrogenation process for preparing furan and alkyl furans comprising subjecting the corresponding tetrahydrofuran to a temperature in the range of 200 to 450C in contact with a catalyst of palladium on carbon.

5 Claims, No Drawings DEHYDROGENATION OF TETRAHYDROFURAN AND ALKY-LSUBSTITUTED TETRAI-IYDROFURANS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a dehydrogenation process for converting tetrahydrofuran and alkyl substituted tetrahydro furans into furan and alkyl substituted furans by means of catalyst system comprising palladium on carbon.

2. Description of the Prior Art It is known that Group VIII noble metals function as hydrogenation and dehydrogenation catalysts for aliphatic hydrocarbons. It is also reported by-N. D. Zelinsky and J. K. .lurjew, Ber 69, 101 (1931) and .I. K. Jerjew and A. E. Borissow, Ber 69, 1395 (1936) that five-membered heterocyclic compounds such as pyrrolidine and thiophan'e can be dehydrogenated on platinum and palladium in the vapor phase to pyrrole and thiophene respectively. Tetrahydrofuran under the same conditions isomerizes with cleavage of the ring forming aliphatic carbonyl compounds. The action of other members of the Group VIII-noble metals (rhodium, osmium, iridium and ruthenium) on carbon with tetrahydrofuran under the same conditions predominately yields isomerization products. For example, it is reported by N. I. Shuikin, l. F Belskii and R. A. Karakhanov, Doklady, Akademii Nauk S.S.S.R., Vol. 138, No. 4, pp. 829-839 May-June 1961, that 2-methyltetrahydrofuran subjected to the action of the Group VIII noble metals mentioned above at 350-400C forms methylpropylketone in 65-70% yield and 2-methylfuran in -20% yield. Since the above mentioned Group VIII- noble metals yield predominately isomerization products, the conclusion to be drawn from the prior art is the palladium catalysts would also lead predominately to isomerization.

With the virtual elimination of lead antiknock compounds and the possible severe limitations in aromatic content of motor fuels, there is a concerted effort by the petroleum industry to find new gasoline octaneimproving compounds. These most sought after additives must be safe and efficient and impart suitable burning characteristics as evidenced by a high octane rating. Furan and alkyl substituted furans have these desirable characteristics. However, the low yields obtained by the prior art methods of converting tetrahydrofurans to furans must be improved to provide the sizeable volume needed and to make such use economically feasible.

SUMMARY OF THE INVENTION I have now found quite unexpectedly that palladium on carbon is a very selective catalyst for the dehydrogenation of tetrahydrofuran and substituted tetrahydrofurans having l-4 alkyl groups and containing 1 to 10 carbon atoms to produce the corresponding furan in yields of around 80% or more. The process comprises subjecting the tetrahydrofuran or substituted furan to a temperature in the range of 200 to 450C in contact with a catalyst system of palladium on carbon.

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the invention the dehydrogenation process can be carried out with tetrahydrofuran or substituted tetrahydrofurans having l-4 alkyl groups and containing from 1-10 carbon atoms in contact with pa]- ladium on carbon. The temperature for the dehydrogenation reaction generally should be in the range of 200 to 450C. and more preferably 275 to 350C. The pressure generally can vary from 0.25 atmosphere to 5 atmospheres. Suitable space rates, in terms of volumes of tetrahydrofuran charge (liquid basis) per volume of catalyst bed per hour are in the range of 0.03 to 4.0. In a preferred embodiment liquid tetrahydrofuran is passed through a bed of the catalyst at the desired space rate and pressure, whereby the dehydrogenation reaction occur to form the desired furans.

A packed bed of 0.5% palladium on 4/8 mesh carbon was used. Particle size and palladium loading are not critical. However, other supports such as alumina, silica gel and barium carbonate give predominately dehydration instead of dehydrogenation.

A flow of hydrogen is needed to prevent catalyst fouling. The life is over 8 hours of continuous running with the selectivity to furan increasing for the first several hours of the run.

Examples of suitable tetrahydrofurans besides tetrahydrofuran which undergo the dehydrogenation pro cess of this invention are 2-methyltetrahydrofuran, 3-methyltetrahydrofuran Z-ethyItetrahydrofuran, B-ethyItetrahydrofuran, 2,5-dimethyltetrahydrofuran (cis and trans), 2,5-methylethyltetrahydrofuran (cis and trans), 2,5-methy1isopropyltetrahydrofuran (cis and trans), 2,5-methylpropyltetrahydrofuran (cis and trans), 2,5-methylbutyltetrahydrofuran (cis and trans), 2,5-methylhexyltetrahydrofuran (cis and trans), 2,5-

methylbutyltetrahydrofuran (cis and trans), 2,5-diethyltetrahydrofuran (cis and trans), 2,5- ethylpropyltetrahydrofuran (cis and trans), 2,5-ethylhexyltetrahydrofuran (cis and trans),

2,5-ethyldecyltetrahydrofuran (cis and trans) and the like. Most preferred are the mono-and di-/methyl and ethyl substituents since they are the most easily obtainable.

The following example illustrates the invention more specifically.

EXAMPLE The reaction was run by passing 0.6 ml.min. of liquid Z-methyItetrahydrofuran over 0.5% Pd on carbon in a 1 inch by 8 inch column. The temperature was 325C and 53 ml/min. of H was simultaneously passed through the column. The reaction products were analyzed as 81% 2-methyl furan and 15% 2-pentanone.

I claim:

l. The dehydrogenation process for preparing furan and substituted furans having 1-4 alkyl groups and containing from 1 to 10 carbon atoms comprising subjecting the corresponding tetrahydrofuran to a temperaaction is carried out in the presence of hydrogen. 

1. THE DEHYDROGENTION PROCESS FOR PREPARING FURAN AND SUBSTITUTED FURANS HAVING 1-4 ALKYL GROUPS AND CONTAINING FROM 1 TO 10 CARBON ATOMS COMPRISING SUBJECTING THE CORRESPONDING TETRAHYDROFURAN TO A TEMPERATTURE IN THE RANGE OF 200 TO 450*C IN CONTACT WITH A CATALYST OF PALLADIUM ON CARBON.
 2. A process according to claim 1 wherein said temperature is in the range of 275 to 350*C.
 3. A process according to claim 1 wherein said tetrahydrofuran is 2-methyltetrahydrofuran.
 4. The dehydrogenation process for preparing 2-methylfuran comprising subjecting 2-methyltetrahydrofuran to a temperature in the range of 275 to 350*C in contact with a catalyst of palladium on carbon.
 5. The process according to claim 1 in which the reaction is carried out in the presence of hydrogen. 